1. Field of the Invention
This invention relates to a multi-fan system separated core engine type turbofan engine comprising at least one core engine and a plurality of propulsion devices.
2. Description of the Prior Art
A conventional turbofan engine is constituted by a fan, a compressor, a combustor, and a turbine, wherein the turbine is driven by using high temperature combustion gas as working fluid produced in the combustor, and the fan is driven by the turbine. This type of turbofan engine is constituted such that the fan and turbine are disposed on the same axis, and therefore the same number of combustors and turbines as fans are necessary to drive the fans. Further, due to restrictions imposed by this disposition, the degree of freedom in the design of these engines is small. Moreover, when turbofan engines of conventional constitutions use a large number of fans in the airframe, the engine constitution becomes complicated, manufacturing costs rise, and operational control of the engine also becomes complicated.
An example of a turbofan engine for solving these problems is disclosed in Japanese Patent Publication No. H5-87655. The turbofan engine disclosed in this publication is a separated core engine type turbofan engine constituted by at least one core engine comprising a compressor, a combustor, and a turbine, and at least one propulsion device which is separated from the core engine and comprises a fan driving combustor which is supplied with high pressure air from the core engine through a high pressure air duct, a turbine, and a fan which is driven by this turbine.
The separated core engine type turbofan engine disclosed in this publication is constituted such that the core engine and propulsion device are disposed and constituted separately, and therefore the propulsion device can be disposed in a desired position without the restriction of being disposed on the same axis as the fan axis and turbine axis. When a separated core engine type turbofan engine of this type is installed in an aircraft, for example, the degree of freedom may be increased and so the desired object may be achieved. However, this propulsion device uses high temperature combustion gas as the working fluid of the turbine for driving the fan, and therefore comprises a fan driving combustor in the interior thereof. As a result, problems arise in that expensive heat-resistant material must be used for the turbine, and propulsion control, including the propulsion device constitution and combustion control, becomes complicated. Thus in this type of separated core engine type turbofan engine, there remains scope for further improvements in fan reliability and manufacturing cost reduction.
The problem that is to be solved in the propulsion device is to alleviate the heat resistance required for the turbine to simplify the constitution and propulsion control of the propulsion device by directly making use of the high pressure air which is supplied from the core engine.
An object of this invention is to provide a multi-fan system separated core engine type turbofan engine which is capable of solving the aforementioned problems in the prior art by using as working fluid on a turbine for driving a fan lower temperature working fluid rather than high temperature combustion gas, thereby eliminating the need to use expensive heat-resistant materials for the turbine and thus reducing the manufacturing costs of the turbofan engine, simplifying the constitution thereof, and also simplifying operational control.
In order to solve the aforementioned problems, the multi-fan system separated core engine type turbofan engine according to this invention is constituted by at least one core engine comprising a compressor, and a combustor and turbine for driving this compressor, and a plurality of propulsion devices disposed separately from the core engine and comprising an air turbine which is driven by high pressure air supplied from the core engine, and a fan which is driven by the air turbine.
According to the multi-fan system separated core engine type turbofan engine constituted in this manner, the turbine is driven by high temperature combustion gas produced in the combustor in at least one of the core engines, the compressor is driven by the output of the combustor, a part of the air compressed by the compressor is transmitted to the combustor, and fuel injected into the combustor is mixed with the air and burned. The remaining part of the high pressure air compressed by the compressor of the core engine is supplied to the plurality of propulsion devices, which are disposed separately to the core engine, to drive the air turbine in the propulsion devices. The output of the air turbine drives the fan so as to obtain thrust. The turbine which drives the fan is an air turbine and does not use combustion gas as working fluid. Therefore a combustor is not provided in the fan driving portion, enabling simplification and size-reduction of the constitution thereof and eliminating the need to use expensive heat-resistant material for the turbine. Engine control is also made easier.
When a plurality of core engines is provided in this separated core engine type turbofan engine, the high pressure air from the core engine may be distributed among and supplied to the plurality of propulsion devices via a common high pressure air control device for controlling temperature, pressure, and so on. When a system constitution comprising a plurality of core engines and a plurality of propulsion devices is provided, the temperature, pressure, flow rate, and so on of the high pressure air from the plurality of core engines are controlled by the common high pressure air control device if irregularities appear in the amounts thereof, and the high pressure air required by the respective propulsion devices is controlled by the high pressure air control device to be distributed among and supplied to the plurality of propulsion devices.
In this multi-fan system separated core engine type turbofan engine, at least a part of the propulsion engines is used for vertical take-off and landing, and therefore this invention can be applied to a vertical take-off and landing aircraft. In other words, when the multi-fan system separated core engine type turbofan engine is applied to a vertical take-off and landing aircraft, at least one part of the propulsion devices may be used for vertical take-off and landing, and the remaining propulsion devices may be used as front and rear direction propulsion devices.